Volcanic And Seismic Events Are Major Pieces Of Evidence Towards Proving That Plate Tectonics Theory Is Valid

Plate tectonic theory was first outlined by Alfred Wegener in 1915 who stated that 200 million years ago the earth used to consist of the single continent of Pangaea which has subsequently split apart forming the seven continents that we recognise today. Wegener explained this phenomenon using the theory of continental drift. He claimed that the lithosphere made up of eight major tectonic plates which float upon a viscous region at the top of the earth s mantle known as the asthenosphere which allowed the plates to move apart. Whilst volcanic events take place where there are fissures in the earth s surface allowing the eruption of molten lava and volcanic gases, seismic events occur when there is a sudden release of energy in the earth s upper mantle. What these two events have in common is that they both occur predominantly on tectonic plate boundaries, thus providing strong evidence that tectonic theory is valid. Yet a wealth of further structural, lithological and paleoclimatic evidence is critical to strengthen this theory as the nature of volcanic and seismic events alone would not be enough to make it irrefutable.

Volcanic and seismic events provide strong evidence that tectonic plate theory is valid by demonstrating that tectonic plates are able to move and therefore the process of continental drift can occur. The best evidence to support this comes from magnetic striping technology which can demonstrate that magma has emerged from underwater volcanoes in the Mid Atlantic Ridge and has forced the ocean floor further and further apart. The technology which was developed by physicist Patrick Blackett who developed the astatic magnenometer which could detect very weak magnetic variations along the ocean floor. Magma consists largely of the rock basalt which has strong magnetic properties and therefore aligns with the earth s magnetic field when it emerges from a plate boundary and solidifies. As the earth s magnetic field flips on average 4-5 times every million years, it is possible to display a series of alternating magnetic stripes which run almost parallel to the plate boundary and indicate that the plates have been moving apart. As the time taken for the magnetic field reversal can be roughly calculated, it is possible to date the strips in order to determine the speed at which the Eurasian and North American plates are separating on this divergent plate boundary. This enables geological specialists to determine the rate at which Pangaea split apart into separate continents and hence proves that Wegener s theory of continental drift was likely to occur.

Seismic events occurring at convergent plate boundaries also provide evidence that tectonic plate theory is valid. Earthquakes are especially prevalent along the Pacific ring of Fire, a seismically active region around the Pacific Ocean where approximately 90% of the world s earthquakes occur. These occcur predominantly along tectonic plate boundaries and are caused by the process of subduction where a denser oceanic plate is forced underneath a continental plate. The fact that differing densities allow plates to subduct proves that the earth s surface made up of tectonic plates must be floating on viscous magma in the asthenospere. The sudden moment of intense ground shaking that occurs during an earthquake is visible evidence of a significant plate movement taking place over a short period of time and therefore proves that plates may have broken away from Pangaea over many millions of years.

Although the location of seismic and tectonic events along plate boundaries provides significant evidence to prove that tectonic plate theory is valid, the location of historic volcanic events that took place in areas now located some distance away from tectonic plate boundaries provides stronger proof that continental drift has occurred. Arthur s Seat, a dormant volcano located outside Edinburgh, last erupted 350 million years ago and now lies 850 miles away from the nearest plate boundary. This therefore demonstrates that Scotland must have sat on a tectonic plate boundary shortly after the breakup of Pangaea and demonstrates that the theory of continental drift must be valid as it has since moved a significant distance away.

The presence of active volcanoes located within today s tectonic plates and not on their boundaries may at first appear to disprove tectonic plate theory. Yellowstone national park for example contains a number of volcanoes including the Caldera which is still thought to be active yet lies hundreds of miles away from the North American Plate boundary. In 1963, Tuzo Wilson came up with the theory of hotspots or small, long lasting and exceptionally hot regions that existed below tectonic plates. These hotspots are able to heat the mantle and allow a persistent stream of magma to emerge which overtime can erupt forming a volcano. The formation of a series of volcanic islands in Hawaii provides excellent demonstration that plates are moving owing to continental drift. Whilst the hotspot remains stationary, the Pacific plate has continued to move so each volcano eventually becomes dormant whilst another forms in its place. Therefore the presence of intra plate volcanoes provides evidence of continental drift and proves that tectonic plate theory is valid.

The use of other geological evidence is, however, essential to provide stronger evidence for the validity of tectonic plate theory. Whilst the changing locations of volcanic and seismic events demonstrates that tectonic plates have moved throughout the course of history, further study of the variations in rock type and the distribution of ancient life forms across the earth s surface is essential to determine the details of these movements and a more precise indication of the exact route these landmasses have travelled.

Lithological evidence or the comparison of different rock types across the earth s surface provides more specific detail of which land masses used to be joined together. Predictably, one would expect similar rock types to be present where two land masses used to be joined together even if they have been separated for millions of years. For example both Brazil and South Africa possess deposits of rare violet quartzes along their respective coastlines which lead us to believe the two land masses were once joined together. Although this feature could merely be a coincidence, the evidence is strengthened by the fact that the Darkensburg Plateau in South Africa are composed of a similar lava to those located in south-eastern Brazil and more importantly, the lava is of a similar thickness. To make the case even more robust, it is possible to consider the stratigraphy or line up of rocks to determine whether there are correlations in rock patterning in different locations. With all these pieces of lithological evidence combined, geologists can be fairly confident in their assertions that certain land masses which now lie thousands of miles apart used to be joined together and this movement can only be explained by tectonic plate theory and continental drift.

Palaentological evidence or the comparison of different life species across the continents also provides evidence that tectonic plate theory is valid. It is possible to compare the fossilised remains of life forms found at different locations to assess whether there are any similarities spread across large geographical distances. For example, remains of the Mesaurus, a small freshwater reptile which lived during the early Permian era between 286 and 258 million years ago, have been found in both South America and Africa. Given the reptiles inability to swim long distances across the saltwater Atlantic Ocean, the reptile must have moved between the two continents when they were closer together or indeed joined. Therefore, the presence of the Mesaurus remains on different continents provides proof that tectonic plates have moved over the course of history and the theory of continental drift is valid.

In conclusion, volcanic and seismic events are major pieces of evidence that tectonic plate theory is valid. The presence of prehistoric volcanic activity away from today s plate boundaries combined with Wilson s theory of volcanic hotspots prove that the earth is made up of moving tectonic plates floating on magma whilst magnetic striping along the Mid Atlantic drift indicates that in some regions these tectonic plates have been moving apart. Yet other lithological and palaentological evidence is required to make the evidence stronger as the seismic and volcanic events only prove that the plates have moved but do not provide further detail the course or nature of their movement. Therefore, whilst volcanic and seismic evidence are the most significant piece of evidence to support tectonic plate theory, other evidence is required to make it irrefutable.